Coordinating snapshot operations across multiple file systems

ABSTRACT

Techniques are provided for coordinating snapshot operations across multiple file systems. A notification may be received that a snapshot of data stored across a persistent memory file system and a storage file system is to be generated. Forwarding, of modify operations from a persistent memory tier to a file system tier for execution through the storage file system, may be enabled. Framing may be initiated to notify the storage file system of blocks within the persistent memory file system that comprise more up-to-date data than corresponding blocks within the storage file system. In response to the framing completing, a consistency point operation is performed to create the snapshot and to create a snapshot image as part of the snapshot.

BACKGROUND

A node, such as a server, a computing device, a virtual machine, a cloudservice, etc., may host a storage operating system. The storageoperating system may be configured to store data on behalf of clientdevices, such as within volumes, aggregates, storage devices, cloudstorage, locally attached storage, etc. In this way, a client can issueread and write operations to the storage operating system of the node inorder to read data from storage or write data to the storage. Thestorage operating system may implement a storage file system throughwhich the data is organized and accessible to the client devices. Thestorage file system may be tailored for managing the storage and accessto data within a particular type of storage media, such asblock-addressable storage media of hard drives, solid state drives,and/or other storage. The storage media and the storage file system maybe managed by a file system tier of the node. The node may also compriseother types of storage media, such as persistent memory that providesrelatively lower latency compared to the storage media managed by thefile system tier. The persistent memory may be byte-addressable, and ismanaged by a persistent memory tier tailored for the performance andpersistence semantics of the persistent memory.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an example computing environmentin which an embodiment of the invention may be implemented.

FIG. 2 is a block diagram illustrating an example of a networkenvironment with exemplary nodes in accordance with an embodiment of theinvention.

FIG. 3 is a block diagram illustrating an example of various componentsthat may be present within a node that may be used in accordance with anembodiment of the invention.

FIG. 4 is a block diagram illustrating an example of various componentsof system for implementing a persistent memory tier and a file systemtier in accordance with an embodiment of the invention.

FIG. 5 is a flow chart illustrating an example of a set of operationsthat support coordinating snapshot operations across multiple filesystems in accordance with an embodiment of the invention.

FIG. 6A is a block diagram illustrating an example of supporting thecoordination of snapshot operations across multiple file systems inaccordance with an embodiment of the invention.

FIG. 6B is a block diagram illustrating an example of supporting thecoordination of snapshot operations across multiple file systems inaccordance with an embodiment of the invention.

FIG. 6C is a block diagram illustrating an example of supporting thecoordination of snapshot operations across multiple file systems inaccordance with an embodiment of the invention.

FIG. 6D is a block diagram illustrating an example of supporting thecoordination of snapshot operations across multiple file systems inaccordance with an embodiment of the invention.

FIG. 7 is a flow chart illustrating an example of a set of operationsthat support coordinating snapshot operations across multiple filesystems in accordance with an embodiment of the invention.

FIG. 8 is a flow chart illustrating an example of a set of operationsthat support coordinating snapshot operations across multiple filesystems in accordance with an embodiment of the invention.

FIG. 9 is an example of a computer readable medium in which anembodiment of the invention may be implemented.

DETAILED DESCRIPTION

The techniques described herein are directed to coordinating snapshotoperations across multiple file systems. A node may expose a singlefrontend file system to clients for storing and accessing data, such aswhere the node exposes a volume, an aggregate, etc. On the backend, dataof the frontend file system may be stored across multiple backend filesystems, such as a persistent memory file system and a storage filesystem.

For example, the node may comprise a persistent memory tier configuredto store data of the frontend file system within persistent memorythrough the persistent memory file system. The node may comprise a filesystem tier configured to store data of the frontend file system withinstorage through a storage file system. The persistent memory may providerelatively lower latency compared to the storage of the file systemtier. Thus, certain data, of the frontend file system, may be copied(tiered) from the storage of the storage file system into the persistentmemory in order to provide client devices with faster access to thecopied data through the persistent memory file system.

The original data may still be maintained within the storage of thestorage file system. As modify operations are executed upon thepersistent memory to change the data within the persistent memory, thedata within the persistent memory may diverge from the original datawithin the storage of the storage file system. In this way, some of thelatest data of the frontend file system may be stored within thepersistent memory (e.g., data within tiered data blocks that have beencopied into the persistent memory and are tracked by the persistentmemory file system), and some of the latest data of the frontend filesystem may be stored within the storage of the storage file system(e.g., non-tiered data blocks that have not been tiered into thepersistent memory and are tracked by the storage file system).

Because two instances of the tiered data of the frontend file system maybe stored across both the storage of the storage file system and thepersistent memory, an original instance of the tiered data within thestorage of the storage file system may become stale/old. The originalinstance of the tiered data may become stale because newer data may havebeen written to the tiered instance of the tiered data within thepersistent memory. To prevent stale data from being provided to clientsor operated upon, the node (e.g., file systems, operating systems, andservices of the node) may be configured to consider data within thepersistent memory as being the authoritative copy for any data blocksthat have been tiered to the persistent memory and are tracked by thepersistent memory file system. This configuration is referred to as aninvariant that is implemented so that client operations can be executedupon the persistent memory comprising the authoritative copy of data sothat clients are not accessing stale/old data. Processing the clientoperations using the persistent memory reduces the latency associatedwith processing the client operations due to the lower latencycharacteristics of the persistent memory.

Performing snapshot operations for the frontend file system ischallenging and complex because data is stored across both persistentmemory and storage of the storage operating system. This is because ofthe use of multiple file systems across different memory tiers. Forexample, some of the latest data may be stored through the persistentmemory file system (e.g., data within tiered data blocks in thepersistent memory), some of the latest data may also be stored throughthe storage file system (e.g., data within non-tiered data blocks in thestorage of the storage file system), and some stale data may be storedthrough the storage file system (e.g., data within data blocks in thestorage of the storage file system that have been tiered into thepersistent memory and subsequently overwritten within the persistentmemory with newer data).

Traditional snapshot operation functionality is unable to create,delete, and/or restore snapshots across multiple file systems, and aremerely configured to operate upon a single file system. Thus, nodes thatimplement a frontend file system backed by multiple backend file systemscannot benefit from snapshot functionality that would otherwise be ableto provide backup and restore functionality for client data.

Accordingly, as provided herein, snapshot creation, deletion, andrestoration is coordinated across multiple file systems of a node inorder to provide backup and restore functionality for client data storedby the node on behalf of client devices. In order to enable thissnapshot functionality across multiple file systems, some embodimentsuse a forwarding mechanism for operations to bypass the persistentmemory tier and a framing mechanism to notify the storage file system ofmore up-to-date data within the persistent memory. These two mechanismsare implemented so that the storage file system becomes aware of thelocation of the more up-to-date data within the persistent memory sothat backup and restore functionality can be implemented by the storagefile system upon the latest data within the persistent memory and thestorage of the storage file system.

The forwarding mechanism is configured to selectively forward certainoperations, such as write operations or operations targeting particularfiles or objects, received by the persistent memory tier to the filesystem tier. The forwarded operations are then executed through thestorage file system upon the storage of the storage file system. As aresult, these forwarded operations bypass being executed through thepersistent memory file system. Without this forwarding mechanism, theoperations would be received by the persistent memory tier, and would beexecuted through the persistent memory file system upon the persistentmemory, thus creating more up-to-date data within the persistent memorythat would need to be communicated to the storage file system.

In some embodiments of forwarding, a modify operation, targeting anobject, is received by the persistent memory tier. The modify operationis compared to a forwarding policy to determine whether forwarding isenabled for the modify operation and the object. If forwarding is notenabled by the forwarding policy, then the modify operation is executedupon the persistent memory through the persistent memory file system. Ifforwarding is enabled by the forwarding policy, then the modifyoperation is forwarded to the file system tier as a forwarded operationthat bypasses the persistent memory file system.

The forwarding policy may enable forwarding for a particular type ofoperation, for a particular object, for a particular time duration,and/or until occurrence of an event such as until a snapshot operationor a framing operation has completed. The forwarded operation can beexecuted through the storage file system upon the storage to write newdata to an instance of the object maintained within the storage. Becausethe instance of the object within the storage now comprises the mostup-to-date data of the object, the now stale data within a correspondinginstance of the object within the persistent memory is deleted. Thispreserves the invariant that if the persistent memory file system istracking and storing data of a data block in the persistent memory, thenthat instance of the data block is the authoritative instance of thedata block compared to a corresponding data block within the storage. Inthis case, the data block of the persistent memory file system is notthe authoritative instance of the data block because the correspondingdata block of the storage file system now comprises the most up-to-datedata (due to the forwarding of certain operations), and thus the datablock is removed from the persistent memory. Removing the data blockfrom the persistent memory preserves the invariant that data within thepersistent memory is the authoritative copy.

Forwarding is performed by the forwarding mechanism in order to preventa backlog, of new data within the persistent memory whose existence hasnot yet been conveyed to the storage file system, from growing. That is,in order for the storage file system to perform a snapshot operation,the storage file system must know where to locate the most up-to-datedata of an object upon which the snapshot operation is beingimplemented.

Without framing used to notify the storage operating system of moreup-to-date data within the persistent memory, new incoming modifyoperations would be executed through the persistent memory file systemto write new data into the persistent memory without the knowledge ofthe storage file system. Thus, framing is performed so that the modifyoperations bypass the persistent memory file system and are forwarded tothe storage file system for execution upon the storage of the storagefile system. In this way, the storage file system will have knowledge ofthe location of the new data within the storage managed by the storagefile system.

In order to notify the storage file system of data blocks within thepersistent memory that comprise more up-to-date data than correspondingblocks within the storage, framing is performed by the framingmechanism. The framing mechanism scans the blocks of the persistentmemory to identify blocks comprising more up-to-date data thancorresponding blocks within the storage of the storage file system.

In some embodiments, the framing mechanism may compare timestamps ofdata within the blocks of the persistent memory to a timestamp of whenframing was last performed. If a timestamp of data within a block of thepersistent memory is newer than the timestamp of when framing was lastperformed, then the block comprises more up-to-date data than acorresponding block within the storage of the storage file system. Insome embodiments, the framing mechanism may identify the blockscomprising the more up-to-date data based upon an indicator such as aflag being set for the blocks to indicate that the blocks comprise newdata not yet framed by the framing mechanism to the storage file system.

For example, when a modify operation is executed by the persistentmemory file system upon the persistent memory to write new data to ablock within the persistent memory, the indicator may be set to indicatethat the block comprises new data not yet framed by the framingmechanism. Once the new data within the block is framed (e.g., theframing mechanism provides the storage file system with a file blocknumber of the block comprising more up-to-date data than a correspondingblock in the storage), the framing mechanism may modify the indicator,such as by clearing the flag. In this way, the framing mechanismidentifies blocks within the persistent memory comprising moreup-to-date data than corresponding blocks within the storage, andtransmits framing operations to the storage file system. The framingoperations comprises file block numbers of these blocks within thepersistent memory so that the storage file system has knowledge of howto access the more up-to-date data.

Once the framing has completed, the storage file system has acomprehensive view of where the latest data of the frontend file systemresides across the persistent memory and the storage of the storage filesystem. The storage file system is able to implement various types ofsnapshot operations, such as snapshot create operations, snapshot deleteoperations, snapshot restore operations, etc. because the storage filesystem is now able to identify where the latest versions of datatargeted by a snapshot operation reside across the persistent memory ofthe persistent memory file system and the storage of the storage filesystem.

Various embodiments of the present technology provide for a wide rangeof technical effects, advantages, and/or improvements to computingsystems and components. For example, various embodiments may include oneor more of the following technical effects, advantages, and/orimprovements: 1) the ability to implement a frontend file system thathas data stored across multiple backend file systems storing data withindiverse types of storage such as block-addressable storage andbyte-addressable storage; 2) the ability to notify a storage file systemof more up-to-date data maintained by a persistent memory file system byutilizing a framing mechanism; 3) the ability to stop a framing backlogfrom increasing by implementing a forwarding mechanism to forwardoperations to the storage file system and bypass the persistent memoryfile system so that the operations do not increase the amount of newdata within the persistent memory to frame; and 4) the ability toimplement various types of snapshot operations across multiple filesystems in order to provide backup and restore functionality for datastored across the multiple file systems.

FIG. 1 is a diagram illustrating an example operating environment 100 inwhich an embodiment of the techniques described herein may beimplemented. In one example, the techniques described herein may beimplemented within a client device 128, such as a laptop, a tablet, apersonal computer, a mobile device, a server, a virtual machine, awearable device, etc. In another example, the techniques describedherein may be implemented within one or more nodes, such as a first node130 and/or a second node 132 within a first cluster 134, a third node136 within a second cluster 138, etc., which may be part of aon-premise, cloud-based, or hybrid storage solution.

A node may comprise a storage controller, a server, an on-premisedevice, a virtual machine such as a storage virtual machine, hardware,software, or combination thereof. The one or more nodes may beconfigured to manage the storage and access to data on behalf of theclient device 128 and/or other client devices. In another example, thetechniques described herein may be implemented within a distributedcomputing platform 102 such as a cloud computing environment (e.g., acloud storage environment, a multi-tenant platform, a hyperscaleinfrastructure comprising scalable server architectures and virtualnetworking, etc.) configured to manage the storage and access to data onbehalf of client devices and/or nodes.

In yet another example, at least some of the techniques described hereinare implemented across one or more of the client device 128, the one ormore nodes 130, 132, and/or 136, and/or the distributed computingplatform 102. For example, the client device 128 may transmitoperations, such as data operations to read data and write data andmetadata operations (e.g., a create file operation, a rename directoryoperation, a resize operation, a set attribute operation, etc.), over anetwork 126 to the first node 130 for implementation by the first node130 upon storage.

The first node 130 may store data associated with the operations withinvolumes or other data objects/structures hosted within locally attachedstorage, remote storage hosted by other computing devices accessibleover the network 126, storage provided by the distributed computingplatform 102, etc. The first node 130 may replicate the data and/or theoperations to other computing devices, such as to the second node 132,the third node 136, a storage virtual machine executing within thedistributed computing platform 102, etc., so that one or more replicasof the data are maintained. For example, the third node 136 may host adestination storage volume that is maintained as a replica of a sourcestorage volume of the first node 130. Such replicas can be used fordisaster recovery and failover.

In an embodiment, the techniques described herein are implemented by astorage operating system or are implemented by a separate module thatinteracts with the storage operating system. The storage operatingsystem may be hosted by the client device, 128, a node, the distributedcomputing platform 102, or across a combination thereof. In someembodiments, the storage operating system may execute within a storagevirtual machine, a hyperscaler, or other computing environment. Thestorage operating system may implement a storage file system tologically organize data within storage devices as one or more storageobjects and provide a logical/virtual representation of how the storageobjects are organized on the storage devices.

A storage object may comprise any logically definable storage elementstored by the storage operating system (e.g., a volume stored by thefirst node 130, a cloud object stored by the distributed computingplatform 102, etc.). Each storage object may be associated with a uniqueidentifier that uniquely identifies the storage object. For example, avolume may be associated with a volume identifier uniquely identifyingthat volume from other volumes. The storage operating system alsomanages client access to the storage objects.

The storage operating system may implement a file system for logicallyorganizing data. For example, the storage operating system may implementa write anywhere file layout for a volume where modified data for a filemay be written to any available location as opposed to a write-in-placearchitecture where modified data is written to the original location,thereby overwriting the previous data. In some embodiments, the filesystem may be implemented through a file system layer that stores dataof the storage objects in an on-disk format representation that isblock-based (e.g., data is stored within 4 kilobyte blocks and inodesare used to identify files and file attributes such as creation time,access permissions, size and block location, etc.).

Deduplication may be implemented by a deduplication module associatedwith the storage operating system. Deduplication is performed to improvestorage efficiency. One type of deduplication is inline deduplicationthat ensures blocks are deduplicated before being written to a storagedevice. Inline deduplication uses a data structure, such as an incorehash store, which maps fingerprints of data to data blocks of thestorage device storing the data. Whenever data is to be written to thestorage device, a fingerprint of that data is calculated and the datastructure is looked up using the fingerprint to find duplicates (e.g.,potentially duplicate data already stored within the storage device). Ifduplicate data is found, then the duplicate data is loaded from thestorage device and a byte-by-byte comparison may be performed to ensurethat the duplicate data is an actual duplicate of the data to be writtento the storage device. If the data to be written is a duplicate of theloaded duplicate data, then the data to be written to disk is notredundantly stored to the storage device.

Instead, a pointer or other reference is stored in the storage device inplace of the data to be written to the storage device. The pointerpoints to the duplicate data already stored in the storage device. Areference count for the data may be incremented to indicate that thepointer now references the data. If at some point the pointer no longerreferences the data (e.g., the deduplicated data is deleted and thus nolonger references the data in the storage device), then the referencecount is decremented. In this way, inline deduplication is able todeduplicate data before the data is written to disk. This improves thestorage efficiency of the storage device.

Background deduplication is another type of deduplication thatdeduplicates data already written to a storage device. Various types ofbackground deduplication may be implemented. In an embodiment ofbackground deduplication, data blocks that are duplicated between filesare rearranged within storage units such that one copy of the dataoccupies physical storage. References to the single copy can be insertedinto a file system structure such that all files or containers thatcontain the data refer to the same instance of the data.

Deduplication can be performed on a data storage device block basis. Inan embodiment, data blocks on a storage device can be identified using aphysical volume block number. The physical volume block number uniquelyidentifies a particular block on the storage device. Additionally,blocks within a file can be identified by a file block number. The fileblock number is a logical block number that indicates the logicalposition of a block within a file relative to other blocks in the file.For example, file block number 0 represents the first block of a file,file block number 1 represents the second block, and the like. Fileblock numbers can be mapped to a physical volume block number that isthe actual data block on the storage device. During deduplicationoperations, blocks in a file that contain the same data are deduplicatedby mapping the file block number for the block to the same physicalvolume block number, and maintaining a reference count of the number offile block numbers that map to the physical volume block number.

For example, assume that file block number 0 and file block number 5 ofa file contain the same data, while file block numbers 1-4 containunique data. File block numbers 1-4 are mapped to different physicalvolume block numbers. File block number 0 and file block number 5 may bemapped to the same physical volume block number, thereby reducingstorage requirements for the file. Similarly, blocks in different filesthat contain the same data can be mapped to the same physical volumeblock number. For example, if file block number 0 of file A contains thesame data as file block number 3 of file B, file block number 0 of fileA may be mapped to the same physical volume block number as file blocknumber 3 of file B.

In another example of background deduplication, a changelog is utilizedto track blocks that are written to the storage device. Backgrounddeduplication also maintains a fingerprint database (e.g., a flatmetafile) that tracks all unique block data such as by tracking afingerprint and other file system metadata associated with block data.Background deduplication can be periodically executed or triggered basedupon an event such as when the changelog fills beyond a threshold. Aspart of background deduplication, data in both the changelog and thefingerprint database is sorted based upon fingerprints. This ensuresthat all duplicates are sorted next to each other. The duplicates aremoved to a dup file.

The unique changelog entries are moved to the fingerprint database,which will serve as duplicate data for a next deduplication operation.In order to optimize certain file system operations needed todeduplicate a block, duplicate records in the dup file are sorted incertain file system sematic order (e.g., inode number and block number).Next, the duplicate data is loaded from the storage device and a wholeblock byte by byte comparison is performed to make sure duplicate datais an actual duplicate of the data to be written to the storage device.After, the block in the changelog is modified to point directly to theduplicate data as opposed to redundantly storing data of the block.

In some embodiments, deduplication operations performed by a datadeduplication layer of a node can be leveraged for use on another nodeduring data replication operations. For example, the first node 130 mayperform deduplication operations to provide for storage efficiency withrespect to data stored on a storage volume. The benefit of thededuplication operations performed on first node 130 can be provided tothe second node 132 with respect to the data on first node 130 that isreplicated to the second node 132. In some aspects, a data transferprotocol, referred to as the LRSE (Logical Replication for StorageEfficiency) protocol, can be used as part of replicating consistencygroup differences from the first node 130 to the second node 132.

In the LRSE protocol, the second node 132 maintains a history bufferthat keeps track of data blocks that the second node 132 has previouslyreceived. The history buffer tracks the physical volume block numbersand file block numbers associated with the data blocks that have beentransferred from first node 130 to the second node 132. A request can bemade of the first node 130 to not transfer blocks that have already beentransferred. Thus, the second node 132 can receive deduplicated datafrom the first node 130, and will not need to perform deduplicationoperations on the deduplicated data replicated from first node 130.

In an embodiment, the first node 130 may preserve deduplication of datathat is transmitted from first node 130 to the distributed computingplatform 102. For example, the first node 130 may create an objectcomprising deduplicated data. The object is transmitted from the firstnode 130 to the distributed computing platform 102 for storage. In thisway, the object within the distributed computing platform 102 maintainsthe data in a deduplicated state. Furthermore, deduplication may bepreserved when deduplicated data is transmitted/replicated/mirroredbetween the client device 128, the first node 130, the distributedcomputing platform 102, and/or other nodes or devices.

In an embodiment, compression may be implemented by a compression moduleassociated with the storage operating system. The compression module mayutilize various types of compression techniques to replace longersequences of data (e.g., frequently occurring and/or redundantsequences) with shorter sequences, such as by using Huffman coding,arithmetic coding, compression dictionaries, etc. For example, anuncompressed portion of a file may comprise “ggggnnnnnnqqqqqqqqqq”,which is compressed to become “4g6n10q”. In this way, the size of thefile can be reduced to improve storage efficiency. Compression may beimplemented for compression groups. A compression group may correspondto a compressed group of blocks. The compression group may berepresented by virtual volume block numbers. The compression group maycomprise contiguous or non-contiguous blocks.

Compression may be preserved when compressed data istransmitted/replicated/mirrored between the client device 128, a node,the distributed computing platform 102, and/or other nodes or devices.For example, an object may be created by the first node 130 to comprisecompressed data. The object is transmitted from the first node 130 tothe distributed computing platform 102 for storage. In this way, theobject within the distributed computing platform 102 maintains the datain a compressed state.

In an embodiment, various types of synchronization may be implemented bya synchronization module associated with the storage operating system.In an embodiment, synchronous replication may be implemented, such asbetween the first node 130 and the second node 132. It may beappreciated that the synchronization module may implement synchronousreplication between any devices within the operating environment 100,such as between the first node 130 of the first cluster 134 and thethird node 136 of the second cluster 138 and/or between a node of acluster and an instance of a node or virtual machine in the distributedcomputing platform 102.

As an example, during synchronous replication, the first node 130 mayreceive a write operation from the client device 128. The writeoperation may target a file stored within a volume managed by the firstnode 130. The first node 130 replicates the write operation to create areplicated write operation. The first node 130 locally implements thewrite operation upon the file within the volume. The first node 130 alsotransmits the replicated write operation to a synchronous replicationtarget, such as the second node 132 that maintains a replica volume as areplica of the volume maintained by the first node 130. The second node132 will execute the replicated write operation upon the replica volumeso that file within the volume and the replica volume comprises the samedata. After, the second node 132 will transmit a success message to thefirst node 130. With synchronous replication, the first node 130 doesnot respond with a success message to the client device 128 for thewrite operation until both the write operation is executed upon thevolume and the first node 130 receives the success message that thesecond node 132 executed the replicated write operation upon the replicavolume.

In another example, asynchronous replication may be implemented, such asbetween the first node 130 and the third node 136. It may be appreciatedthat the synchronization module may implement asynchronous replicationbetween any devices within the operating environment 100, such asbetween the first node 130 of the first cluster 134 and the distributedcomputing platform 102. In an embodiment, the first node 130 mayestablish an asynchronous replication relationship with the third node136. The first node 130 may capture a baseline snapshot of a firstvolume as a point in time representation of the first volume. The firstnode 130 may utilize the baseline snapshot to perform a baselinetransfer of the data within the first volume to the third node 136 inorder to create a second volume within the third node 136 comprisingdata of the first volume as of the point in time at which the baselinesnapshot was created.

After the baseline transfer, the first node 130 may subsequently createsnapshots of the first volume over time. As part of asynchronousreplication, an incremental transfer is performed between the firstvolume and the second volume. In particular, a snapshot of the firstvolume is created. The snapshot is compared with a prior snapshot thatwas previously used to perform the last asynchronous transfer (e.g., thebaseline transfer or a prior incremental transfer) of data to identify adifference in data of the first volume between the snapshot and theprior snapshot (e.g., changes to the first volume since the lastasynchronous transfer). Accordingly, the difference in data isincrementally transferred from the first volume to the second volume. Inthis way, the second volume will comprise the same data as the firstvolume as of the point in time when the snapshot was created forperforming the incremental transfer. It may be appreciated that othertypes of replication may be implemented, such as semi-sync replication.

In an embodiment, the first node 130 may store data or a portion thereofwithin storage hosted by the distributed computing platform 102 bytransmitting the data within objects to the distributed computingplatform 102. In one example, the first node 130 may locally storefrequently accessed data within locally attached storage. Lessfrequently accessed data may be transmitted to the distributed computingplatform 102 for storage within a data storage tier 108. The datastorage tier 108 may store data within a service data store 120, and maystore client specific data within client data stores assigned to suchclients such as a client (1) data store 122 used to store data of aclient (1) and a client (N) data store 124 used to store data of aclient (N). The data stores may be physical storage devices or may bedefined as logical storage, such as a virtual volume, LUNs, or otherlogical organizations of data that can be defined across one or morephysical storage devices. In another example, the first node 130transmits and stores all client data to the distributed computingplatform 102. In yet another example, the client device 128 transmitsand stores the data directly to the distributed computing platform 102without the use of the first node 130.

The management of storage and access to data can be performed by one ormore storage virtual machines (SVMs) or other storage applications thatprovide software as a service (SaaS) such as storage software services.In one example, an SVM may be hosted within the client device 128,within the first node 130, or within the distributed computing platform102 such as by the application server tier 106. In another example, oneor more SVMs may be hosted across one or more of the client device 128,the first node 130, and the distributed computing platform 102. The oneor more SVMs may host instances of the storage operating system.

In an embodiment, the storage operating system may be implemented forthe distributed computing platform 102. The storage operating system mayallow client devices to access data stored within the distributedcomputing platform 102 using various types of protocols, such as aNetwork File System (NFS) protocol, a Server Message Block (SMB)protocol and Common Internet File System (CIFS), and Internet SmallComputer Systems Interface (iSCSI), and/or other protocols. The storageoperating system may provide various storage services, such as disasterrecovery (e.g., the ability to non-disruptively transition clientdevices from accessing a primary node that has failed to a secondarynode that is taking over for the failed primary node), backup andarchive function, replication such as asynchronous and/or synchronousreplication, deduplication, compression, high availability storage,cloning functionality (e.g., the ability to clone a volume, such as aspace efficient flex clone), snapshot functionality (e.g., the abilityto create snapshots and restore data from snapshots), data tiering(e.g., migrating infrequently accessed data to slower/cheaper storage),encryption, managing storage across various platforms such as betweenon-premise storage systems and multiple cloud systems, etc.

In one example of the distributed computing platform 102, one or moreSVMs may be hosted by the application server tier 106. For example, aserver (1) 116 is configured to host SVMs used to execute applicationssuch as storage applications that manage the storage of data of theclient (1) within the client (1) data store 122. Thus, an SVM executingon the server (1) 116 may receive data and/or operations from the clientdevice 128 and/or the first node 130 over the network 126. The SVMexecutes a storage application and/or an instance of the storageoperating system to process the operations and/or store the data withinthe client (1) data store 122. The SVM may transmit a response back tothe client device 128 and/or the first node 130 over the network 126,such as a success message or an error message. In this way, theapplication server tier 106 may host SVMs, services, and/or otherstorage applications using the server (1) 116, the server (N) 118, etc.

A user interface tier 104 of the distributed computing platform 102 mayprovide the client device 128 and/or the first node 130 with access touser interfaces associated with the storage and access of data and/orother services provided by the distributed computing platform 102. In anembodiment, a service user interface 110 may be accessible from thedistributed computing platform 102 for accessing services subscribed toby clients and/or nodes, such as data replication services, applicationhosting services, data security services, human resource services,warehouse tracking services, accounting services, etc. For example,client user interfaces may be provided to corresponding clients, such asa client (1) user interface 112, a client (N) user interface 114, etc.The client (1) can access various services and resources subscribed toby the client (1) through the client (1) user interface 112, such asaccess to a web service, a development environment, a human resourceapplication, a warehouse tracking application, and/or other services andresources provided by the application server tier 106, which may usedata stored within the data storage tier 108.

The client device 128 and/or the first node 130 may subscribe to certaintypes and amounts of services and resources provided by the distributedcomputing platform 102. For example, the client device 128 may establisha subscription to have access to three virtual machines, a certainamount of storage, a certain type/amount of data redundancy, a certaintype/amount of data security, certain service level agreements (SLAs)and service level objectives (SLOs), latency guarantees, bandwidthguarantees, access to execute or host certain applications, etc.Similarly, the first node 130 can establish a subscription to haveaccess to certain services and resources of the distributed computingplatform 102.

As shown, a variety of clients, such as the client device 128 and thefirst node 130, incorporating and/or incorporated into a variety ofcomputing devices may communicate with the distributed computingplatform 102 through one or more networks, such as the network 126. Forexample, a client may incorporate and/or be incorporated into a clientapplication (e.g., software) implemented at least in part by one or moreof the computing devices.

Examples of suitable computing devices include personal computers,server computers, desktop computers, nodes, storage servers, nodes,laptop computers, notebook computers, tablet computers or personaldigital assistants (PDAs), smart phones, cell phones, and consumerelectronic devices incorporating one or more computing devicecomponents, such as one or more electronic processors, microprocessors,central processing units (CPU), or controllers. Examples of suitablenetworks include networks utilizing wired and/or wireless communicationtechnologies and networks operating in accordance with any suitablenetworking and/or communication protocol (e.g., the Internet). In usecases involving the delivery of customer support services, the computingdevices noted represent the endpoint of the customer support deliveryprocess, i.e., the consumer's device.

The distributed computing platform 102, such as a multi-tenant businessdata processing platform or cloud computing environment, may includemultiple processing tiers, including the user interface tier 104, theapplication server tier 106, and a data storage tier 108. The userinterface tier 104 may maintain multiple user interfaces, includinggraphical user interfaces and/or web-based interfaces. The userinterfaces may include the service user interface 110 for a service toprovide access to applications and data for a client (e.g., a “tenant”)of the service, as well as one or more user interfaces that have beenspecialized/customized in accordance with user specific requirements(e.g., as discussed above), which may be accessed via one or more APIs.

The service user interface 110 may include components enabling a tenantto administer the tenant's participation in the functions andcapabilities provided by the distributed computing platform 102, such asaccessing data, causing execution of specific data processingoperations, etc. Each processing tier may be implemented with a set ofcomputers, virtualized computing environments such as a storage virtualmachine or storage virtual server, and/or computer components includingcomputer servers and processors, and may perform various functions,methods, processes, or operations as determined by the execution of asoftware application or set of instructions.

The data storage tier 108 may include one or more data stores, which mayinclude the service data store 120 and one or more client data stores122-124. Each client data store may contain tenant-specific data that isused as part of providing a range of tenant-specific business andstorage services or functions, including but not limited to ERP, CRM,eCommerce, Human Resources management, payroll, storage services, etc.Data stores may be implemented with any suitable data storagetechnology, including structured query language (SQL) based relationaldatabase management systems (RDBMS), file systems hosted by operatingsystems, object storage, etc.

In accordance with one embodiment of the invention, the distributedcomputing platform 102 may be a multi-tenant and service platformoperated by an entity in order to provide multiple tenants with a set ofbusiness related applications, data storage, and functionality. Theseapplications and functionality may include ones that a business uses tomanage various aspects of its operations. For example, the applicationsand functionality may include providing web-based access to businessinformation systems, thereby allowing a user with a browser and anInternet or intranet connection to view, enter, process, or modifycertain types of business information or any other type of information.

A clustered network environment 200 that may implement one or moreaspects of the techniques described and illustrated herein is shown inFIG. 2 . The clustered network environment 200 includes data storageapparatuses 202(1)-202(n) that are coupled over a cluster or clusterfabric 204 that includes one or more communication network(s) andfacilitates communication between the data storage apparatuses202(1)-202(n) (and one or more modules, components, etc. therein, suchas, nodes 206(1)-206(n), for example), although any number of otherelements or components can also be included in the clustered networkenvironment 200 in other examples. This technology provides a number ofadvantages including methods, non-transitory computer readable media,and computing devices that implement the techniques described herein.

In this example, nodes 206(1)-206(n) can be primary or local storagecontrollers or secondary or remote storage controllers that provideclient devices 208(1)-208(n) with access to data stored within datastorage devices 210(1)-210(n) and cloud storage device(s) 236 (alsoreferred to as cloud storage node(s)). The nodes 206(1)-206(n) may beimplemented as hardware, software (e.g., a storage virtual machine), orcombination thereof.

The data storage apparatuses 202(1)-202(n) and/or nodes 206(1)-206(n) ofthe examples described and illustrated herein are not limited to anyparticular geographic areas and can be clustered locally and/or remotelyvia a cloud network, or not clustered in other examples. Thus, in oneexample the data storage apparatuses 202(1)-202(n) and/or node computingdevice 206(1)-206(n) can be distributed over a plurality of storagesystems located in a plurality of geographic locations (e.g., locatedon-premise, located within a cloud computing environment, etc.); whilein another example a clustered network can include data storageapparatuses 202(1)-202(n) and/or node computing device 206(1)-206(n)residing in a same geographic location (e.g., in a single on-site rack).

In the illustrated example, one or more of the client devices208(1)-208(n), which may be, for example, personal computers (PCs),computing devices used for storage (e.g., storage servers), or othercomputers or peripheral devices, are coupled to the respective datastorage apparatuses 202(1)-202(n) by network connections 212(1)-212(n).Network connections 212(1)-212(n) may include a local area network (LAN)or wide area network (WAN) (i.e., a cloud network), for example, thatutilize TCP/IP and/or one or more Network Attached Storage (NAS)protocols, such as a Common Internet File system (CIFS) protocol or aNetwork File system (NFS) protocol to exchange data packets, a StorageArea Network (SAN) protocol, such as Small Computer System Interface(SCSI) or Fiber Channel Protocol (FCP), an object protocol, such assimple storage service (S3), and/or non-volatile memory express (NVMe),for example.

Illustratively, the client devices 208(1)-208(n) may be general-purposecomputers running applications and may interact with the data storageapparatuses 202(1)-202(n) using a client/server model for exchange ofinformation. That is, the client devices 208(1)-208(n) may request datafrom the data storage apparatuses 202(1)-202(n) (e.g., data on one ofthe data storage devices 210(1)-210(n) managed by a network storagecontroller configured to process I/O commands issued by the clientdevices 208(1)-208(n)), and the data storage apparatuses 202(1)-202(n)may return results of the request to the client devices 208(1)-208(n)via the network connections 212(1)-212(n).

The nodes 206(1)-206(n) of the data storage apparatuses 202(1)-202(n)can include network or host nodes that are interconnected as a clusterto provide data storage and management services, such as to anenterprise having remote locations, cloud storage (e.g., a storageendpoint may be stored within cloud storage device(s) 236), etc., forexample. Such nodes 206(1)-206(n) can be attached to the cluster fabric204 at a connection point, redistribution point, or communicationendpoint, for example. One or more of the nodes 206(1)-206(n) may becapable of sending, receiving, and/or forwarding information over anetwork communications channel, and could comprise any type of devicethat meets any or all of these criteria.

In an embodiment, the nodes 206(1) and 206(n) may be configuredaccording to a disaster recovery configuration whereby a surviving nodeprovides switchover access to the data storage devices 210(1)-210(n) inthe event a disaster occurs at a disaster storage site (e.g., the nodecomputing device 206(1) provides client device 212(n) with switchoverdata access to data storage devices 210(n) in the event a disasteroccurs at the second storage site). In other examples, the nodecomputing device 206(n) can be configured according to an archivalconfiguration and/or the nodes 206(1)-206(n) can be configured based onanother type of replication arrangement (e.g., to facilitate loadsharing). Additionally, while two nodes are illustrated in FIG. 2 , anynumber of nodes or data storage apparatuses can be included in otherexamples in other types of configurations or arrangements.

As illustrated in the clustered network environment 200, nodes206(1)-206(n) can include various functional components that coordinateto provide a distributed storage architecture. For example, the nodes206(1)-206(n) can include network modules 214(1)-214(n) and disk modules216(1)-216(n). Network modules 214(1)-214(n) can be configured to allowthe nodes 206(1)-206(n) (e.g., network storage controllers) to connectwith client devices 208(1)-208(n) over the storage network connections212(1)-212(n), for example, allowing the client devices 208(1)-208(n) toaccess data stored in the clustered network environment 200.

Further, the network modules 214(1)-214(n) can provide connections withone or more other components through the cluster fabric 204. Forexample, the network module 214(1) of node computing device 206(1) canaccess the data storage device 210(n) by sending a request via thecluster fabric 204 through the disk module 216(n) of node computingdevice 206(n) when the node computing device 206(n) is available.Alternatively, when the node computing device 206(n) fails, the networkmodule 214(1) of node computing device 206(1) can access the datastorage device 210(n) directly via the cluster fabric 204. The clusterfabric 204 can include one or more local and/or wide area computingnetworks (i.e., cloud networks) embodied as Infiniband, Fibre Channel(FC), or Ethernet networks, for example, although other types ofnetworks supporting other protocols can also be used.

Disk modules 216(1)-216(n) can be configured to connect data storagedevices 210(1)-210(n), such as disks or arrays of disks, SSDs, flashmemory, or some other form of data storage, to the nodes 206(1)-206(n).Often, disk modules 216(1)-216(n) communicate with the data storagedevices 210(1)-210(n) according to the SAN protocol, such as SCSI orFCP, for example, although other protocols can also be used. Thus, asseen from an operating system on nodes 206(1)-206(n), the data storagedevices 210(1)-210(n) can appear as locally attached. In this manner,different nodes 206(1)-206(n), etc. may access data blocks, files, orobjects through the operating system, rather than expressly requestingabstract files.

While the clustered network environment 200 illustrates an equal numberof network modules 214(1)-214(n) and disk modules 216(1)-216(n), otherexamples may include a differing number of these modules. For example,there may be a plurality of network and disk modules interconnected in acluster that do not have a one-to-one correspondence between the networkand disk modules. That is, different nodes can have a different numberof network and disk modules, and the same node computing device can havea different number of network modules than disk modules.

Further, one or more of the client devices 208(1)-208(n) can benetworked with the nodes 206(1)-206(n) in the cluster, over the storageconnections 212(1)-212(n). As an example, respective client devices208(1)-208(n) that are networked to a cluster may request services(e.g., exchanging of information in the form of data packets) of nodes206(1)-206(n) in the cluster, and the nodes 206(1)-206(n) can returnresults of the requested services to the client devices 208(1)-208(n).In one example, the client devices 208(1)-208(n) can exchangeinformation with the network modules 214(1)-214(n) residing in the nodes206(1)-206(n) (e.g., network hosts) in the data storage apparatuses202(1)-202(n).

In one example, the storage apparatuses 202(1)-202(n) host aggregatescorresponding to physical local and remote data storage devices, such aslocal flash or disk storage in the data storage devices 210(1)-210(n),for example. One or more of the data storage devices 210(1)-210(n) caninclude mass storage devices, such as disks of a disk array. The disksmay comprise any type of mass storage devices, including but not limitedto magnetic disk drives, flash memory, and any other similar mediaadapted to store information, including, for example, data and/or parityinformation.

The aggregates include volumes 218(1)-218(n) in this example, althoughany number of volumes can be included in the aggregates. The volumes218(1)-218(n) are virtual data stores or storage objects that define anarrangement of storage and one or more file systems within the clusterednetwork environment 200. Volumes 218(1)-218(n) can span a portion of adisk or other storage device, a collection of disks, or portions ofdisks, for example, and typically define an overall logical arrangementof data storage. In one example, volumes 218(1)-218(n) can includestored user data as one or more files, blocks, or objects that mayreside in a hierarchical directory structure within the volumes218(1)-218(n).

Volumes 218(1)-218(n) are typically configured in formats that may beassociated with particular storage systems, and respective volumeformats typically comprise features that provide functionality to thevolumes 218(1)-218(n), such as providing the ability for volumes218(1)-218(n) to form clusters, among other functionality. Optionally,one or more of the volumes 218(1)-218(n) can be in composite aggregatesand can extend between one or more of the data storage devices210(1)-210(n) and one or more of the cloud storage device(s) 236 toprovide tiered storage, for example, and other arrangements can also beused in other examples.

In one example, to facilitate access to data stored on the disks orother structures of the data storage devices 210(1)-210(n), a filesystem may be implemented that logically organizes the information as ahierarchical structure of directories and files. In this example,respective files may be implemented as a set of disk blocks of aparticular size that are configured to store information, whereasdirectories may be implemented as specially formatted files in whichinformation about other files and directories are stored.

Data can be stored as files or objects within a physical volume and/or avirtual volume, which can be associated with respective volumeidentifiers. The physical volumes correspond to at least a portion ofphysical storage devices, such as the data storage devices 210(1)-210(n)(e.g., a Redundant Array of Independent (or Inexpensive) Disks (RAIDsystem)) whose address, addressable space, location, etc. does notchange. Typically, the location of the physical volumes does not changein that the range of addresses used to access it generally remainsconstant.

Virtual volumes, in contrast, can be stored over an aggregate ofdisparate portions of different physical storage devices. Virtualvolumes may be a collection of different available portions of differentphysical storage device locations, such as some available space fromdisks, for example. It will be appreciated that since the virtualvolumes are not “tied” to any one particular storage device, virtualvolumes can be said to include a layer of abstraction or virtualization,which allows it to be resized and/or flexible in some regards.

Further, virtual volumes can include one or more logical unit numbers(LUNs), directories, Qtrees, files, and/or other storage objects, forexample. Among other things, these features, but more particularly theLUNs, allow the disparate memory locations within which data is storedto be identified, for example, and grouped as data storage unit. Assuch, the LUNs may be characterized as constituting a virtual disk ordrive upon which data within the virtual volumes is stored within anaggregate. For example, LUNs are often referred to as virtual drives,such that they emulate a hard drive, while they actually comprise datablocks stored in various parts of a volume.

In one example, the data storage devices 210(1)-210(n) can have one ormore physical ports, wherein each physical port can be assigned a targetaddress (e.g., SCSI target address). To represent respective volumes, atarget address on the data storage devices 210(1)-210(n) can be used toidentify one or more of the LUNs. Thus, for example, when one of thenodes 206(1)-206(n) connects to a volume, a connection between the oneof the nodes 206(1)-206(n) and one or more of the LUNs underlying thevolume is created.

Respective target addresses can identify multiple of the LUNs, such thata target address can represent multiple volumes. The I/O interface,which can be implemented as circuitry and/or software in a storageadapter or as executable code residing in memory and executed by aprocessor, for example, can connect to volumes by using one or moreaddresses that identify the one or more of the LUNs.

Referring to FIG. 3 , node computing device 206(1) in this particularexample includes processor(s) 300, a memory 302, a network adapter 304,a cluster access adapter 306, and a storage adapter 308 interconnectedby a system bus 310. In other examples, the node computing device 206(1)comprises a virtual machine, such as a virtual storage machine. The nodecomputing device 206(1) also includes a storage operating system 312installed in the memory 302 that can, for example, implement a RAID dataloss protection and recovery scheme to optimize reconstruction of dataof a failed disk or drive in an array, along with other functionalitysuch as deduplication, compression, snapshot creation, data mirroring,synchronous replication, asynchronous replication, encryption, etc. Insome examples, the node computing device 206(n) is substantially thesame in structure and/or operation as node computing device 206(1),although the node computing device 206(n) can also include a differentstructure and/or operation in one or more aspects than the nodecomputing device 206(1).

The network adapter 304 in this example includes the mechanical,electrical and signaling circuitry needed to connect the node computingdevice 206(1) to one or more of the client devices 208(1)-208(n) overnetwork connections 212(1)-212(n), which may comprise, among otherthings, a point-to-point connection or a shared medium, such as a localarea network. In some examples, the network adapter 304 furthercommunicates (e.g., using TCP/IP) via the cluster fabric 204 and/oranother network (e.g., a WAN) (not shown) with cloud storage device(s)236 to process storage operations associated with data stored thereon.

The storage adapter 308 cooperates with the storage operating system 312executing on the node computing device 206(1) to access informationrequested by one of the client devices 208(1)-208(n) (e.g., to accessdata on a data storage device 210(1)-210(n) managed by a network storagecontroller). The information may be stored on any type of attached arrayof writeable media such as magnetic disk drives, flash memory, and/orany other similar media adapted to store information.

In the exemplary data storage devices 210(1)-210(n), information can bestored in data blocks on disks. The storage adapter 308 can include I/Ointerface circuitry that couples to the disks over an I/O interconnectarrangement, such as a storage area network (SAN) protocol (e.g., SmallComputer System Interface (SCSI), Internet SCSI (iSCSI), hyperSCSI,Fiber Channel Protocol (FCP)). The information is retrieved by thestorage adapter 308 and, if necessary, processed by the processor(s) 300(or the storage adapter 308 itself) prior to being forwarded over thesystem bus 310 to the network adapter 304 (and/or the cluster accessadapter 306 if sending to another node computing device in the cluster)where the information is formatted into a data packet and returned to arequesting one of the client devices 208(1)-208(2) and/or sent toanother node computing device attached via the cluster fabric 204. Insome examples, a storage driver 314 in the memory 302 interfaces withthe storage adapter to facilitate interactions with the data storagedevices 210(1)-210(n).

The storage operating system 312 can also manage communications for thenode computing device 206(1) among other devices that may be in aclustered network, such as attached to a cluster fabric 204. Thus, thenode computing device 206(1) can respond to client device requests tomanage data on one of the data storage devices 210(1)-210(n) or cloudstorage device(s) 236 (e.g., or additional clustered devices) inaccordance with the client device requests.

The file system module 318 of the storage operating system 312 canestablish and manage one or more file systems including software codeand data structures that implement a persistent hierarchical namespaceof files and directories, for example. As an example, when a new datastorage device (not shown) is added to a clustered network system, thefile system module 318 is informed where, in an existing directory tree,new files associated with the new data storage device are to be stored.This is often referred to as “mounting” a file system.

In the example node computing device 206(1), memory 302 can includestorage locations that are addressable by the processor(s) 300 andadapters 304, 306, and 308 for storing related software application codeand data structures. The processor(s) 300 and adapters 304, 306, and 308may, for example, include processing elements and/or logic circuitryconfigured to execute the software code and manipulate the datastructures.

The storage operating system 312, portions of which are typicallyresident in the memory 302 and executed by the processor(s) 300, invokesstorage operations in support of a file service implemented by the nodecomputing device 206(1). Other processing and memory mechanisms,including various computer readable media, may be used for storingand/or executing application instructions pertaining to the techniquesdescribed and illustrated herein. For example, the storage operatingsystem 312 can also utilize one or more control files (not shown) to aidin the provisioning of virtual machines.

In this particular example, the memory 302 also includes a moduleconfigured to implement the techniques described herein, as discussedabove and further below.

The examples of the technology described and illustrated herein may beembodied as one or more non-transitory computer or machine readablemedia, such as the memory 302, having machine or processor-executableinstructions stored thereon for one or more aspects of the presenttechnology, which when executed by processor(s), such as processor(s)300, cause the processor(s) to carry out the steps necessary toimplement the methods of this technology, as described and illustratedwith the examples herein. In some examples, the executable instructionsare configured to perform one or more steps of a method described andillustrated later.

FIG. 4 illustrates a system 400 comprising node 402 that implements afile system tier 424 to manage storage 426 and a persistent memory tier422 to manage persistent memory 416 of the node 402. The node 402 maycomprise a server, an on-premise device, a virtual machine, computingresources of a cloud computing environment (e.g., a virtual machinehosted within the cloud), a computing device, hardware, software, orcombination thereof. The node 402 may be configured to manage thestorage and access of data on behalf of clients, such as a client device428. The node 402 may host a storage operating system configured tostore and manage data within and/or across various types of storagedevices, such as locally attached storage, cloud storage, disk storage,flash storage, solid state drives, tape, hard disk drives, etc. Forexample, the storage operating system of the node 402 may store datawithin storage 426, which may be composed of one or more types ofblock-addressable storage (e.g., disk drive, a solid-state drive, etc.)or other types of storage. The data may be stored within storageobjects, such as volumes, containers, logical unit numbers (LUNs),aggregates, cloud storage objects, etc. In an embodiment, an aggregateor other storage object may be comprised of physical storage of a singlestorage device or storage of multiple storage devices or storageproviders.

The storage operating system of the node 402 may implement a storagefile system 418 that manages the storage and client access of datawithin the storage objects stored within the storage 426 associated withthe node 402. For example, the client device 428 may utilize the storagefile system 418 in order to create, delete, organize, modify, and/oraccess files within directories of a volume managed by the storage filesystem 418. The storage operating system may be associated with astorage operating system storage stack 420 that comprises a plurality oflevels through which operations, such as read and write operations fromclient devices, are processed. An operation may first be processed by ahighest-level tier, and then down through lower-level tiers of thestorage operating system storage stack 420 until reaching a lowest leveltier of the storage operating system storage stack 420. The storage filesystem 418 may be managed by a file system tier 424 within the storageoperating system storage stack 420. When an operation reaches the filesystem tier 424, the operation may be processed by the storage filesystem 418 for storage within the storage 426.

The storage file system 418 may be configured with commands, APIs, datastructures (e.g., data structures used to identify block addresslocations of data within the storage 426), and/or other functionality(e.g., functionality to access certain block ranges within the storage426) that is tailored to the block-addressable storage 426. Because thestorage file system 418 is tailored for the block-addressable semanticsof the storage 426, the storage file system 418 may be unable to utilizeother types of storage that use a different addressing semantics such aspersistent memory 416 that is byte-addressable. The persistent memory416 provides relatively lower latency and faster access speeds than theblock-addressable storage 426 that the storage file system 418 isnatively tailored to manage. Because the persistent memory 416 isbyte-addressable instead of block-addressable, the storage file system418, data structures of the storage file system 418 used to locate dataaccording to block-addressable semantics of the storage 426, and thecommands to store and retrieved data from the block-addressable storage426 may not be able to be leveraged for the byte-addressable persistentmemory 416.

Accordingly, a persistent memory file system 414 and the persistentmemory tier 422 for managing the persistent memory file system 414 areimplemented for the persistent memory 416 so that the node 402 can usethe persistent memory file system 414 to access and manage thepersistent memory 416 or other types of byte-addressable storage forstoring user data. The persistent memory 416 may comprise memory that ispersistent, such that data structures can be stored in a manner wherethe data structures can continue to be accessed using memoryinstructions and/or memory APIs even after the end of a process thatcreated or last modified the data structures. The data structures anddata will persist even in the event of a power loss, failure and reboot,etc.

The persistent memory 416 is non-volatile memory that has nearly thesame speed and latency of DRAM and has the non-volatility of NAND flash.The persistent memory 416 could dramatically increase system performanceof the node 402 compared to the higher latency and slower speeds of theblock-addressable storage 426 accessible to the node 402 through thestorage file system 418 using the file system tier 424 (e.g., hard diskdrives, solid state storage, cloud storage, etc.). The persistent memory416 is byte-addressable, and may be accessed through a memorycontroller. This provides faster and more fine-grained access topersistent storage within the persistent memory 416 compared toblock-based access to the block-addressable storage 426 through thestorage file system 418.

The persistent memory file system 414 implemented for thebyte-addressable persistent memory 416 is different than the storagefile system 418 implemented for the block-addressable storage 426. Forexample, the persistent memory file system 414 may comprise datastructures and/or functionality tailored to byte-addressable semanticsof the persistent memory 416 for accessing bytes of storage, which aredifferent than data structures and functionality of the storage filesystem 418 that are tailored to block-addressable semantics of thestorage 426 for accessing blocks of storage. Furthermore, the persistentmemory file system 414 is tailored for the relatively faster accessspeeds and lower latency of the persistent memory 416, which improvesthe operation of the node 402 by allowing the node 402 to process I/Ofrom client devices much faster using the persistent memory tier 422,the persistent memory file system 414, and the persistent memory 416.

In order to integrate the persistent memory 416 into the node 402 in amanner that allows client data of client devices, such as the clientdevice 428, to be stored into and read from the persistent memory 416,the persistent memory tier 422 is implemented within the storageoperating system storage stack 420 for managing the persistent memory416. The persistent memory tier 422 is maintained at a higher levelwithin the storage operating system storage stack 420 than the filesystem tier 424 used to manage the storage file system 418. Thepersistent memory tier 422 is maintained higher in the storage operatingsystem storage stack 420 than the file system tier 424 so thatoperations received from client devices by the node 402 are processed bythe persistent memory tier 422 before the file system tier 424 eventhough the operations may target the storage file system 418 managed bythe file system tier 424. This occurs because higher levels within thestorage operation system storage stack 420 process operations beforelower levels within the storage operating system storage stack 420.

The persistent memory tier 422 may implement various APIs,functionality, data structures, metadata, and commands for thepersistent memory file system 414 to access and/or manage the persistentmemory 416. For example, the persistent memory tier 422 may implementAPIs to access the persistent memory file system 414 of the persistentmemory 416 for storing data into and/or retrieving data from thepersistent memory 416 according to byte-addressable semantics of thepersistent memory 416. The persistent memory tier 422 may implementfunctionality to determine when data should be tiered out from thepersistent memory 416 to the storage 426 based upon the data becominginfrequently accessed, and thus cold.

The persistent memory file system 414 is configured with data structuresand/or metadata for tracking and locating data within the persistentmemory 416 according to the byte-addressable semantics. For example, thepersistent memory file system 414 indexes the persistent memory 416 ofthe node 402 as an array of pages (e.g., 4 kb pages) indexed by pageblock numbers. One of the pages, such as a page (1), comprises a filesystem superblock that is a root of a file system tree (a buffer tree)of the persistent memory file system 414. A duplicate copy of the filesystem superblock may be maintained within another page of thepersistent memory 416 (e.g., a last page, a second to last page, a pagethat is a threshold number of indexed pages away from page (1), etc.).The file system superblock comprises a location of a list of file systeminfo objects 404.

The list of file system info objects 404 comprises a linked list ofpages, where each page contains a set of file system info objects. Ifthere are more file system info objects than what can be stored within apage, then additional pages may be used to store the remaining filesystem info objects and each page will have a location of the next pageof file system info objects. In this way, a plurality of file systeminfo objects can be stored within a page of the persistent memory 416.Each file system info object defines a file system instance for a volumeand snapshot (e.g., a first file system info object correspond to anactive file system of the volume, a second file system info object maycorrespond to a first snapshot of the volume, a third file system infoobject may correspond to a second snapshot of the volume, etc.). Eachfile system info object comprises a location within the persistentmemory 416 of an inofile (e.g., a root of a page tree of the inofile)comprising inodes of a file system instance.

An inofile 406 of the file system instance comprises an inode for eachfile within the file system instance. An inode of a file comprisesmetadata about the file. Each inode stores a location of a root of afile tree for a given file. In particular, the persistent memory filesystem 414 maintains file trees 408, where each file is represented by afile tree of indirect pages (intermediate nodes of the file tree) anddirect blocks (leaf nodes of the file tree). The direct blocks arelocated in a bottom level of the file tree, and one or more levels ofindirect pages are located above the bottom level of the file tree. Theindirect pages of a particular level comprise references to blocks in anext level down within the file tree (e.g., a reference comprising apage block number of a next level down node or a reference comprising aper-page structure ID of a per-page structure having the page blocknumber of the next level down node). Direct blocks are located at alowest level in the file tree and comprise user data. Thus, a file treefor a file may be traversed by the persistent memory file system 414using a byte range (e.g., a byte range specified by an I/O operation)mapped to a page index of a page (e.g., a 4 k offset) comprising thedata within the file to be accessed.

The persistent memory file system 414 may maintain other data structuresand/or metadata used to track and locate data within the persistentmemory 416. In an embodiment, the persistent memory file system 414maintains per-page structures 410. A per-page structure is used to trackmetadata about each page within the persistent memory 416. Each pagewill correspond to a single per-page structure that comprises metadataabout the page. In an embodiment, the per-page structures are stored inan array within the persistent memory 416. The per-page structurescorrespond to file system superblock pages, file system info pages,indirect pages of the inofile 406, user data pages within the file trees408, per-page structure array pages, etc.

In an embodiment of implementing per-page structure to page mappingsusing a one-to-one mapping, a per-page structure for a page can be fixedat a page block number offset within a per-page structure table. In anembodiment of implementing per-page structure to page mappings using avariable mapping, a per-page structure of a page stores a page blocknumber of the page represented by the per-page structure. With thevariable mapping, persistent memory objects (e.g., objects stored withinthe file system superblock to point to the list of file system infoobjects; objects within a file system info object to point to the rootof the inofile; objects within an inode to point to a root of a filetree of a file; and objects within indirect pages to point to childblocks (child pages)) will store a per-page structure ID of its per-pagestructure as a location of a child page being pointed to, and willredirect through the per-page structure using the per-page structure IDto identify the physical block number of the child page being pointedto. Thus, an indirect entry of an indirect page will comprise a per-pagestructure ID that can be used to identify a per-page structure having aphysical block number of the page child pointed to by the indirect page.

The persistent memory tier 422 may implement functionality to utilize apolicy to determine whether certain operations should be redirected tothe persistent memory file system 414 and the persistent memory 416 orto the storage file system 418 and the storage 426 (e.g., if a writeoperation targets a file that the policy predicts will be accessedagain, such as accessed within a threshold timespan or accessed above acertain frequency, then the write operation will be retargeted to thepersistent memory 416). For example, the node 402 may receive anoperation from the client device 428.

The operation may be processed by the storage operating system using thestorage operating system storage stack 420 from a highest level downthrough lower levels of the storage operating system storage stack 420.Because the persistent memory tier 422 is at a higher level within thestorage operating system storage stack 420 than the file system tier424, the operation is intercepted by the persistent memory tier 422before reaching the file system tier 424. The operation is interceptedby the persistent memory tier 422 before reaching the file system tier424 even though the operation may target the storage file system 418managed by the file system tier 424. This is because the persistentmemory tier 422 is higher in the storage operating system storage stack420 than the file system tier 424, and operations are processed byhigher levels before lower levels within the storage operating systemstorage stack 420.

Accordingly, the operation is intercepted by the persistent memory tier422 within the storage operating system storage stack 420. Thepersistent memory tier 422 may determine whether the operation is to beretargeted to the persistent memory file system 414 and the persistentmemory 416 or whether the operation is to be transmitted (e.g., releasedto lower tiers within the storage operating system storage stack 420) bythe persistent memory tier 422 to the file system tier 424 forprocessing by the storage file system 418 utilizing the storage 426. Inthis way, the tiers within the storage operating system storage stack420 are used to determine how to route and process operations utilizingthe persistent memory 416 and/or the storage 426.

In an embodiment, an operation 401 is received by the node 402. Theoperation 401 may comprise a file identifier of a file to be accessed.The operation 401 may comprise file system instance information, such asa volume identifier of a volume to be accessed and/or a snapshotidentifier of a snapshot of the volume to be accessed. If an active filesystem of the volume is to be accessed, then the snapshot identifier maybe empty, null, missing, comprising a zero value, or otherwisecomprising an indicator that no snapshot is to be accessed. Theoperation 401 may comprise a byte range of the file to be accessed.

The list of file system info objects 404 is evaluated using the filesystem information to identify a file system info object matching thefile system instance information. That is, the file system info objectmay correspond to an instance of the volume (e.g., the active filesystem of the volume or a snapshot identified by the snapshot identifierof the volume identified by the volume identifier within the operation401) being targeted by the operation 401, which is referred to as aninstance of a file system or a file system instance. In an embodiment ofthe list of file system info objects 404, the list of file system infoobjects 404 is maintained as a linked list of entries. Each entrycorresponds to a file system info object, and comprises a volumeidentifier and a snapshot identifier of the file system info object. Inresponse to the list of file system info objects 404 not comprising anyfile system info objects that match the file system instanceinformation, the operation 401 is routed to the file system tier 424 forexecution by the storage file system 418 upon the block-addressablestorage 426 because the file system instance is not tiered into thepersistent memory 416. However, if the file system info object matchingthe file system instance information is found, then the file system infoobject is evaluated to identify an inofile such as the inofile 406 ascomprising inodes representing files of the file system instancetargeted by the operation 401.

The inofile 406 is traversed to identify an inode matching the fileidentifier specified by the operation 401. The inofile 406 may berepresented as a page tree having levels of indirect pages (intermediatenodes of the page tree) pointing to blocks within lower levels (e.g., aroot points to level 2 indirect pages, the level 2 indirect pages pointto level 1 indirect pages, and the level 1 indirect pages point to level0 direct blocks). The page tree has a bottom level (level 0) of directblocks (leaf nodes of the page tree) corresponding to the inodes of thefile. In this way, the indirect pages within the inofile 406 aretraversed down until a direct block corresponding to an inode having thefile identifier of the file targeted by the operation 401 is located.

The inode may be utilized by the persistent memory file system 414 tofacilitate execution of the operation 401 by the persistent memory tier422 upon the persistent memory 416 in response to the inode comprisingan indicator (e.g., a flag, a bit, etc.) specifying that the file istiered into the persistent memory 416 of the node 402. If the indicatorspecifies that the file is not tiered into the persistent memory 416 ofthe node 402, then the operation 401 is routed to the file system tier424 for execution by the storage file system 418 upon theblock-addressable storage 426.

In an embodiment where the operation 401 is a read operation and theinode comprises an indicator that the file is tiered into the persistentmemory 416, the inode is evaluated to identify a pointer to a file treeof the file. The file tree may comprise indirect pages (intermediatenodes of the file tree comprising references to lower nodes within thefile tree) and direct blocks (leaf nodes of the file tree comprisinguser data of the file). The file tree may be traversed down throughlevels of the indirect pages to a bottom level of direct blocks in orderto locate one or more direct blocks corresponding to pages within thepersistent memory 416 comprising data to be read by the read operation(e.g., a direct block corresponding to the byte range specified by theoperation 401). That is, the file tree may be traversed to identify datawithin one or more pages of the persistent memory 416 targeted by theread operation. The traversal utilizes the byte range specified by theread operation. The byte range is mapped to a page index of a page(e.g., a 4 kb offset) of the data within the file to be accessed by theread operation. In an embodiment, the file tree is traversed todetermine whether the byte range is present within the persistent memory416. If the byte range is present, then the read operation is executedupon the byte range. If the byte range is not present, then the readoperation is routed to the file system tier 424 for execution by thestorage file system 418 upon the block-based storage 426 because thebyte range to be read is not stored within the persistent memory 416. Ifa portion of the byte range is present within the persistent memory 416,then the remaining portion of the byte range is retrieved from thestorage 426.

In an embodiment where the operation 401 is a write operation, accesspattern history of the file (e.g., how frequently and recently the filehas been accessed) is evaluated in order to determine whether theexecute the write operation upon the persistent memory 416 or to routethe write operation to the file system tier 424 for execution by thestorage file system 418 upon the block-addressable storage 426. In thisway, operations are selectively redirected by the persistent memory tier422 to the persistent memory file system 414 for execution upon thebyte-addressable persistent memory 416 or routed to the file system tier424 for execution by the storage file system 418 upon theblock-addressable storage 426 based upon the access pattern history(e.g., write operations targeting more frequently or recently accesseddata/files may be executed against the persistent memory 416).

One embodiment of coordinating snapshot operations across multiple filesystems is illustrated by an exemplary method 500 of FIG. 5 and furtherdescribed in conjunction with system 600 of FIGS. 6A-6D. The node 602may comprise a persistent memory tier 608 associated with persistentmemory 606 of the node 602 and a file system tier 610 associated withstorage 614 managed by the node 602, similar to node 402 of FIG. 4 . Thenode 602 may implement a persistent memory file system 604 used tostore, organize, and provide access to data within the persistent memory606. The node 602 may implement a storage file system 612 to store,organize, and provide access to data within the storage 614 managed bythe node 602.

In some embodiments, the node 602 may expose a single frontend filesystem of a storage object (e.g., a volume, an aggregate, etc.) to aclient. On the backend of the node 602, the data of the frontend filesystem is stored across the persistent memory 606 through the persistentmemory file system 604 and the storage 614 through the storage filesystem 612. For example, the node 602 may expose a volume to a clientdevice. Data blocks within the storage 614 of the storage file system612 may be allocated for the volume. At least some corresponding datablocks may be allocated within pages of the persistent memory 606 by thepersistent memory file system 604. Some of the data within the storage614 of the storage file system 612 may be copied (tiered) from datablocks within the storage 614 into corresponding data blocks within thepersistent memory 606, and thus two instances of the data are storedacross the storage 614 by the storage file system 612 and the persistentmemory 606 by the persistent memory file system 604. Because thepersistent memory 606 provides lower latency than the storage 614 of thestorage file system 612, operations targeting the frontend file system,such as the volume, may be intercepted by the persistent memory tier 608before reaching the file system tier 610. Instead of these operationsbeing implemented by the storage file system 612 upon the storage 614,the operations may be implemented by the persistent memory file system604 upon the persistent memory 606 so that client experienced latency isreduced.

As operations are executed by the persistent memory file system 604 uponthe persistent memory 606, data within blocks of the persistent memory606 may diverge from data within corresponding blocks of the storage 614of the storage file system 612. Because these operations are executedupon the persistent memory 606 by the persistent memory file system 604and are not executed by the storage file system 612 upon the storage614, an invariant may be imposed. The invariant may specify that theauthoritative copy of data is to be maintained within the persistentmemory 606 by the persistent memory file system 604 for blocks that havebeen tiered into the persistent memory 606 and are tracked by thepersistent memory file system 604 (e.g., not all blocks are tiered intothe persistent memory 606, and thus the authoritative copy of theseblocks are in the storage 614 and tracked by the storage file system612).

When operations, such as modify operations, are executed through thepersistent memory file system 604 to write new data to blocks within thepersistent memory 606, the storage file system 612 is unaware of the newdata that now makes corresponding blocks within the storage 614 comprisestale data. Thus, the storage file system 612 would be unable toimplement snapshot operations because the storage file system 612 isunaware of the fact that new data of an object targeted by a snapshotoperation is stored within the persistent memory 606. Accordingly, asprovided herein, a framing mechanism and a forwarding mechanism areimplemented in order to make the storage file system 612 aware of themore up-to-date data and locations such as file block numbers of blockswithin the persistent memory 606 comprising the more up-to-date data sothat the storage file system 612 may implement the storage operations onthe more up-to-date data as opposed to stale data within the storage614.

During operation 502 of method 500 of FIG. 5 , the persistent memorytier 608 may receive a notification 616 from the file system tier 610that the storage file system 612 is implementing snapshot creationfunctionality to generate a snapshot associated with the frontend filesystem whose data is stored across the persistent memory file system 604and the storage file system 612, as illustrated by FIG. 6A. For example,a client device may transmit a snapshot creation request to the node 602for creating a snapshot of the volume (the frontend file system) usingsnapshot functionality hosted by the file system tier 610. In anotherexample, a backup policy for the volume may specify that the snapshot ofthe volume is to be created using the snapshot functionality hosted bythe file system tier 610. In this way, the file system tier 610 mayreceive a snapshot creation request, such as from the client or due tothe backup policy, to create the snapshot. Accordingly, the file systemtier 610 may transmit the notification 616 to the persistent memory tier608 that the snapshot is to be created. In some embodiments, the filesystem tier 610 may be configured to fail any subsequently receivedsnapshot requests until the snapshot is created.

During operation 504 of method 500 of FIG. 5 , the persistent memorytier 608 may enable forwarding of modify operations to bypass thepersistent memory file system 604, as illustrated by FIG. 6B. In someembodiments, the persistent memory tier 608 may generate a forwardingpolicy 624 based upon the notification 616 received from the file systemtier 610. The forwarding policy 624 may specify that modify operationsreceived by the persistent memory tier 608 and targeting the volume forwhich the snapshot is to be created are to be forwarded to the filesystem 610 as forwarded operations for execution through the storagefile system 612 and are to bypass execution through the persistentmemory file system 604. The forwarding policy 624 may be defined with aforwarding duration window indicating that the forwarding policy 624 isto be enforced until the snapshot has been created.

In an example, the node 602 may receive a modify operation 622 from aclient device 620. The modify operation 622 may target a data blockwithin the volume, and is to write new data into the data block. Aninstance of the data block may be maintained within the persistentmemory 606 and a corresponding instance of the data block may bemaintained within the storage 614. If forwarding was not enabled, thepersistent memory tier 608 would execute the modify operation 622through the persistent memory file system 604 to write the new data tothe block within the persistent memory 606. However, this would increasea framing backlog of new data in the persistent memory 606 that is to beframed to the file system tier 610 so that the snapshot can be created.In this way, forwarding is enabled so that the framing backlog does notkeep increasing, thus allowing a framing technique to work through theframing backlog to completion.

As part of forwarding the modify operation 622, the persistent memorytier 608 determines that the forwarding policy 624 enables forwardingfor the modify operation 622 and the target object (e.g., the data blockof the volume) targeted by the modify operation 622. Accordingly, thepersistent memory tier 608 refrains from executing the modify operation622 through the persistent memory file system 604 upon the persistentmemory 606. Instead, the persistent memory tier 608 forwards the modifyoperation 622 to the file system tier 610 as a forwarded operation 626.The file system tier 610 may log the forwarded operation 626 into a log,such as an NVLog. The file system tier 610 may execute the forwardedoperation 626 through the storage file system 612 to write the new datato the corresponding data block within the storage 614, thus leaving thedata within the data block in the persistent memory 606 stale. In orderto enforce the variant that the authoritative copy of data for datablocks, tiered into the persistent memory 606, is to be maintainedwithin the persistent memory 606, the stale data is deleted from thedata block in the persistent memory 606 in response to the forwardedoperation 626 being logged into the log. Because the forwarded operation626 is executed through the storage file system 612 to write the newdata to the storage 614 of the storage file system 612, the storage filesystem 612 is aware of the latest version of the data of the targetobject being this new data. Thus, the storage file system 612 cansubsequently execute the snapshot creation operation to target the newdata within the corresponding data block in the storage 614.

In some embodiments, the node 602 may perform a remote direct accessmemory transfer to notify a partner node that the new data has beenwritten into the storage 614 and/or to notify the partner node that thestale data is being removed from the persistent memory 606. In this way,the partner node, which may maintain a mirrored copy of the content inthe persistent memory of the node 602 within its own partner persistentmemory of the partner node, may make corresponding modifications to thepartner persistent memory. In this way, the partner persistent memory ofthe partner node may mirror the persistent memory of the node 602 sothat if the node 602 fails, then the partner node can takeoverprocessing client operations in place of the failed node 602 using themirrored data within the partner persistent memory of the partner node.

During operation 506 of method 500 of FIG. 5 , framing may be initiatedby the persistent memory tier 608, as illustrated by FIG. 6C. Theframing is performed to notify the storage file system 612 and/or thefile system tier 610 of blocks stored in the persistent memory 606 andmanaged by the persistent memory file system 604 because these blockscomprise more up-to-date data than corresponding blocks stored withinthe storage 614. During framing, a block within the persistent memory606 may be identified as having more up-to-date data than acorresponding block in the storage 614 such as where an indicator wasset, when the persistent memory file system 604 executed a modifyoperation to write new data to the block, in order to indicate that theblock has the new data that has not yet been framed to the file systemtier 610. Accordingly, a file block number of the block in thepersistent memory 606 may be transmitted in a framing operation 630 fromthe persistent memory tier 608 to the file system tier 610 so that thestorage file system 612 can utilize the file block number to referenceand/or retrieve the more up-to-date data such as during execution of thesnapshot creation operation. In some embodiments, a timer may beimplemented for the framing. If the timer times out before the framingcompletes, then the framing may be aborted.

During operation 508 of method 500 of FIG. 5 , in response to theframing completing, a consistency point operation for the storage filesystem 612 is performed to create 640 the snapshot through the storagefile system 612 and to create 642 a snapshot image through thepersistent memory file system 604 as part of the snapshot, asillustrated by FIG. 6D. When the persistent memory file system 604creates 642 the snapshot image, a hierarchical reference may be added tothe snapshot image. In some embodiments, if there are any remote directaccess memory transfers from the persistent memory file system 604 ofthe node 602 to the partner persistent memory file system of a partnernode, then the consistent point operation is suspended until the remotedirect access memory transfers are complete and until there are no otherpending remote direct access memory transfers. That is, the partner nodemay maintain, within the partner persistent memory of the partner node,a mirror copy of the data within the persistent memory 606 of the node602 so that if the node 602 ever fails, then the partner node can takeover the processing of operations from client devices in place of thefailed node 602 using the mirrored data within the partner persistentmemory. Thus, the consistency point operation will wait until allpending remote direct access memory transfers are complete beforeproceeding so that the persistent memory 606 of the node 602 and thepartner persistent memory of the partner node mirror one another and arein-sync.

In some embodiments, a pending operation may be received during thecreation 640 of the snapshot and/or the creation 642 of the snapshotimage. The pending operation may be atomically implemented to eitherfully execute against the snapshot such that all operations of thepending operation are included within the snapshot or the pendingoperation is fully executed against an active file system for which thesnapshot is being created such that all operations are part of theactive file system and not the snapshot. In this way, the pendingoperation is restricted from having some operations of the pendingoperation execute against and being part of the snapshot, while otheroperations of the pending operation are executed against the active filesystem and are not part of the snapshot.

In response to the snapshot being created 640 and the snapshot imagebeing created 642 as part of the snapshot, the forwarding of modifyoperations may be disabled so that incoming modify operations may beexecuted through the persistent memory file system 604 to the persistentmemory 606. For example, the forwarding policy 624 may be removed inorder to disable the forwarding of the modify operations.

In some embodiments, an access request such as a read operation may bereceived by the node 602. The access request may target data that ispart of the snapshot and/or the snapshot image. If the access requesttargets data within the snapshot that is located in the storage 614,then the data is retrieved through the storage file system 612 from thestorage 614. If the access request targets data within the snapshotimage of the snapshot that is located within the persistent memory 606,then a file block number, which was previously provided to the filesystem tier 610 by framing, is used to access a block within thepersistent memory 606 corresponding to the file block number in order toretrieve the data. In some embodiments, all of the data being requestedby the access request may be located within and retrieved from thesnapshot within the storage 614. In some embodiments, all of the databeing requested by the access request may be located within andretrieved from the snapshot image within the persistent memory 606. Insome embodiments, a first portion of the data being requested by theaccess request may be located within and retrieved from the snapshotwithin the storage 614 and a second portion of the data being requestedby the access request may be located within and retrieved from thesnapshot image within the persistent memory 606.

In some embodiments, snapshot creation state information may bemaintained to track various states relating to the performance of asnapshot operation. The snapshot creation state information may comprisea first state. In some embodiments, the first state or another state mayindicate whether the storage file system 612 has received a snapshotrequest to create the snapshot. In some embodiments, the first state oranother state may indicate whether the persistent memory file system 604has been notified by the storage file system 612, such as through thenotification 616, that the snapshot is to be created. The snapshotcreation state information may comprise a second state. In someembodiments, the second state or another state may indicate whether thepersistent memory file system 604 has enabled forwarding or not. In someembodiments, the second state or another state may indicate whether thepersistent memory file system 604 has initiated framing. In someembodiments, the second state or another state may indicate whether thepersistent memory file system 604 has notified the storage file system612 that framing is complete. The snapshot creation state informationmay comprise a third state. In some embodiments, the third state oranother state indicates whether the consistency point operation hasinitiated to create 640 the snapshot. In some embodiments, the thirdstate or another state indicates whether the persistent memory filesystem 604 has been notified to create 642 the snapshot image. In someembodiments, the third state or another state indicates whether thepersistent memory file system 604 has disabled forwarding. In someembodiments, the third state or another state indicates whether theconsistency point operation has created 640 the snapshot. In this way,the snapshot creation state information may be used to track and controlthe implementation of snapshot operations. It may be appreciated thatthe snapshot creation state information may comprise any number ofstates.

One embodiment of coordinating snapshot operations across multiple filesystems is illustrated by an exemplary method 700 of FIG. 7 , which isdescribed in relation to the system 600 of FIG. 6D. During operation 702of method 700 of FIG. 7 , the storage file system 612 may receive asnapshot request to delete the snapshot corresponding to data storedacross the persistent memory 606 by the persistent memory file system604 as the snapshot image and data stored across the storage 614 by thestorage file system 612 as the snapshot. Accordingly, the storage filesystem 612 may delete the snapshot from the storage 614 at the storagefile system 612.

During operation 704 of method 700 of FIG. 7 , in response to thesnapshot being deleted at the storage file system 612, a reference,within a namespace of the persistent memory file system 604, to thesnapshot image that was part of the snapshot is removed. In this way,the snapshot image is unlinked from the persistent memory file system604.

During operation 706 of method 700 of FIG. 7 , the snapshot image may bequeued for subsequent deletion of data blocks of the snapshot image fromthe persistent memory file system 604 (e.g., deletion of the data withinthe data blocks in the persistent memory 606 that correspond to thesnapshot image) after the reference has been removed from the namespace.This allows the data blocks of the snapshot image to be deleted at asubsequent point in time, such as when additional processing resourcesare available or during a timeframe when utilization of the node 602 isbelow a threshold (e.g., lazy deletion of the data blocks).

Client operations may be processed while the snapshot image is queuedfor subsequent deletion of the data from the data blocks within thepersistent memory 606, and thus the deletion of the snapshot image isnon-blocking with respect to client I/O. Furthermore, the snapshotrequest may be acknowledged as complete while the snapshot image isqueued for subsequent deletion so that processing of the snapshotrequest is not unduly delayed. The snapshot request can be acknowledgedas complete because the reference to the snapshot has already beenremoved from the namespace. Subsequent to acknowledging the snapshotrequest as complete, the persistent memory file system 604 may betraversed to free pages within the persistent memory 606 that comprisethe data blocks of data of the snapshot image that is being deleted. Inthis way, the snapshot request to delete the snapshot may be quicklyperformed without blocking client I/O, and the freeing of the pageswithin the persistent memory 606 for storing other data can be lazilyperformed such as when there is adequate resource availability and/orlow utilization of the node 602.

One embodiment of coordinating snapshot operations across multiple filesystems is illustrated by an exemplary method 800 of FIG. 8 , which isdescribed in relation to the system 600 of FIG. 6D. During operation 802of method 800 of FIG. 8 , a restore request to restore the persistentmemory file system 604 and the storage file system 612 of the node 602(e.g., restore an active file system of the node 602, such as thefrontend file system) to a state of the snapshot and snapshot image maybe received. Accordingly, a fence may be implemented for the persistentmemory file system 604 and the storage file system 612 to blockoperations directed to the persistent memory file system 604 and thestorage file system 612. During operation 804 of method 800 of FIG. 8 ,once the persistent memory file system 604 and the storage file system612 are fenced, the storage file system 612 is restored to the state ofthe snapshot. During operation 806 of method 800 of FIG. 8 , thepersistent memory file system 604 is restored to a state of the snapshotimage that is part of the snapshot. During operation 808 of method 800of FIG. 8 , once the persistent memory file system 604 and the storagefile system 612 have been restored to the states of the snapshot andsnapshot image, the persistent memory file system 604 and the storagefile system 612 are unfenced to allow execution operations directed tothe persistent memory file system 604 and the storage file system 612.In some embodiments, a reference count of the snapshot image may beincreased so that the active file system associated with the persistentmemory file system 604 points to the snapshot image. In this way, thefrontend file system is restored to the state of the snapshot andsnapshot image.

In some embodiments, the node 602 may experience a failure (e.g., akernel panic, a crash, etc.) during implementation of the restorerequest. Accordingly, state information, associated with theimplementation of the restore request, may be cleared from thepersistent memory file system 604. In an example, a snapshot restoreoperation of the restore request is implemented and managed by thestorage file system 612. The storage file system 612 first performs thesnapshot restore operation upon the storage file system 612. After thispoint, if the storage file system 612 experiences a failure, such as bypanicking, before a next consistency point that would persist thesnapshot restore operation for the storage file system 612 to persistentstorage, then the snapshot restore operation is rejected in the storagefile system 612. State information corresponding to various states ofimplementing the restore request (e.g., states relating to theoperations of method 800) may be used to detect that the snapshotrestore operation did not completed. This state information, which wastracked within the persistent memory file system 604 during apreparation phase of the snapshot restore operation, may be cleared(e.g., rejected or rolled back). In some embodiments where the restorerequest was to restore a volume, the state information may be clearedwhen the volume is mounted after reboot of the node 602 from thefailure.

Still another embodiment involves a computer-readable medium 900comprising processor-executable instructions configured to implement oneor more of the techniques presented herein. An example embodiment of acomputer-readable medium or a computer-readable device that is devisedin these ways is illustrated in FIG. 9 , wherein the implementationcomprises a computer-readable medium 908, such as a compactdisc-recordable (CD-R), a digital versatile disc-recordable (DVD-R),flash drive, a platter of a hard disk drive, etc., on which is encodedcomputer-readable data 906. This computer-readable data 906, such asbinary data comprising at least one of a zero or a one, in turncomprises processor-executable computer instructions 904 configured tooperate according to one or more of the principles set forth herein. Insome embodiments, the processor-executable computer instructions 904 areconfigured to perform a method 902, such as at least some of theexemplary method 500 of FIG. 5 , at least some of the exemplary method700 of FIG. 7 , and/or at least some of the exemplary method 800 of FIG.8 , for example. In some embodiments, the processor-executable computerinstructions 904 are configured to implement a system, such as at leastsome of the exemplary system 600 of FIGS. 6A-6D, for example. Many suchcomputer-readable media are contemplated to operate in accordance withthe techniques presented herein.

In an embodiment, the described methods and/or their equivalents may beimplemented with computer executable instructions. Thus, in anembodiment, a non-transitory computer readable/storage medium isconfigured with stored computer executable instructions of analgorithm/executable application that when executed by a machine(s)cause the machine(s) (and/or associated components) to perform themethod. Example machines include but are not limited to a processor, acomputer, a server operating in a cloud computing system, a serverconfigured in a Software as a Service (SaaS) architecture, a smartphone, and so on. In an embodiment, a computing device is implementedwith one or more executable algorithms that are configured to performany of the disclosed methods.

It will be appreciated that processes, architectures and/or proceduresdescribed herein can be implemented in hardware, firmware and/orsoftware. It will also be appreciated that the provisions set forthherein may apply to any type of special-purpose computer (e.g., filehost, storage server and/or storage serving appliance) and/orgeneral-purpose computer, including a standalone computer or portionthereof, embodied as or including a storage system. Moreover, theteachings herein can be configured to a variety of storage systemarchitectures including, but not limited to, a network-attached storageenvironment and/or a storage area network and disk assembly directlyattached to a client or host computer. Storage system should thereforebe taken broadly to include such arrangements in addition to anysubsystems configured to perform a storage function and associated withother equipment or systems.

In some embodiments, methods described and/or illustrated in thisdisclosure may be realized in whole or in part on computer-readablemedia. Computer readable media can include processor-executableinstructions configured to implement one or more of the methodspresented herein, and may include any mechanism for storing this datathat can be thereafter read by a computer system. Examples of computerreadable media include (hard) drives (e.g., accessible via networkattached storage (NAS)), Storage Area Networks (SAN), volatile andnon-volatile memory, such as read-only memory (ROM), random-accessmemory (RAM), electrically erasable programmable read-only memory(EEPROM) and/or flash memory, compact disk read only memory (CD-ROM)s,CD-Rs, compact disk re-writeable (CD-RW)s, DVDs, cassettes, magnetictape, magnetic disk storage, optical or non-optical data storage devicesand/or any other medium which can be used to store data.

Some examples of the claimed subject matter have been described withreference to the drawings, where like reference numerals are generallyused to refer to like elements throughout. In the description, forpurposes of explanation, numerous specific details are set forth inorder to provide an understanding of the claimed subject matter. It maybe evident, however, that the claimed subject matter may be practicedwithout these specific details. Nothing in this detailed description isadmitted as prior art.

Although the subject matter has been described in language specific tostructural features or methodological acts, it is to be understood thatthe subject matter defined in the appended claims is not necessarilylimited to the specific features or acts described above. Rather, thespecific features and acts described above are disclosed as exampleforms of implementing at least some of the claims.

Various operations of embodiments are provided herein. The order inwhich some or all of the operations are described should not beconstrued to imply that these operations are necessarily orderdependent. Alternative ordering will be appreciated given the benefit ofthis description. Further, it will be understood that not all operationsare necessarily present in each embodiment provided herein. Also, itwill be understood that not all operations are necessary in someembodiments.

Furthermore, the claimed subject matter is implemented as a method,apparatus, or article of manufacture using standard application orengineering techniques to produce software, firmware, hardware, or anycombination thereof to control a computer to implement the disclosedsubject matter. The term “article of manufacture” as used herein isintended to encompass a computer application accessible from anycomputer-readable device, carrier, or media. Of course, manymodifications may be made to this configuration without departing fromthe scope or spirit of the claimed subject matter.

As used in this application, the terms “component”, “module,” “system”,“interface”, and the like are generally intended to refer to acomputer-related entity, either hardware, a combination of hardware andsoftware, software, or software in execution. For example, a componentincludes a process running on a processor, a processor, an object, anexecutable, a thread of execution, an application, or a computer. By wayof illustration, both an application running on a controller and thecontroller can be a component. One or more components residing within aprocess or thread of execution and a component may be localized on onecomputer or distributed between two or more computers.

Moreover, “exemplary” is used herein to mean serving as an example,instance, illustration, etc., and not necessarily as advantageous. Asused in this application, “or” is intended to mean an inclusive “or”rather than an exclusive “or”. In addition, “a” and “an” as used in thisapplication are generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Also, at least one of A and B and/or the like generally means A orB and/or both A and B. Furthermore, to the extent that “includes”,“having”, “has”, “with”, or variants thereof are used, such terms areintended to be inclusive in a manner similar to the term “comprising”.

Many modifications may be made to the instant disclosure withoutdeparting from the scope or spirit of the claimed subject matter. Unlessspecified otherwise, “first,” “second,” or the like are not intended toimply a temporal aspect, a spatial aspect, an ordering, etc. Rather,such terms are merely used as identifiers, names, etc. for features,elements, items, etc. For example, a first set of information and asecond set of information generally correspond to set of information Aand set of information B or two different or two identical sets ofinformation or the same set of information.

Also, although the disclosure has been shown and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others skilled in the art based upon a reading andunderstanding of this specification and the annexed drawings. Thedisclosure includes all such modifications and alterations and islimited only by the scope of the following claims. In particular regardto the various functions performed by the above described components(e.g., elements, resources, etc.), the terms used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure. In addition, while aparticular feature of the disclosure may have been disclosed withrespect to only one of several implementations, such feature may becombined with one or more other features of the other implementations asmay be desired and advantageous for any given or particular application.

What is claimed is:
 1. A method comprising: in response to receiving a notification that a snapshot of data stored across a persistent memory file system and a storage file system of a node is to be generated, enabling forwarding of modify operations from received by a persistent memory tier that manages the persistent memory file system, wherein the forwarding includes: bypassing execution through the persistent memory file system of an operation received at the persistent memory tier; and forwarding, from the persistent memory tier, the operation to a storage file system tier for execution by the storage file system; initiating framing to cause the persistent memory file system to notify the storage file system of blocks within the persistent memory file system that comprise more up-to-date data than corresponding blocks within the storage file system; and in response to the framing completing, creating the snapshot through the storage file system, wherein the snapshot includes a snapshot image created by the persistent memory file system to include the more up-to-date data, wherein the forwarding is disabled in response to the snapshot being created.
 2. The method of claim 1, comprising: in response to the snapshot being created and the forwarding of the modify operations removing stale data from the persistent memory, disabling the forwarding of incoming modify operations so that the incoming modify operations are executed upon the persistent memory file system.
 3. The method of claim 1, comprising: implementing a timer for a framing process that scans the persistent memory to identify and frame the blocks within the persistent memory file system that comprise the more up-to-date data, wherein the framing process is aborted based upon the timer timing out.
 4. The method of claim 1, comprising: in response to receiving an access request to access first data within the snapshot, retrieving the first data from the storage file system based upon a determination that the first data is stored through the storage file system.
 5. The method of claim 4, comprising: in response to the access request targeting second data within the snapshot, utilizing a file block number, provided to the storage file system by the framing, to access a block within the persistent memory file system comprising the second data.
 6. The method of claim 1, comprising: failing subsequently received snapshot requests until the snapshot is created.
 7. The method of claim 1, comprising: in response to identifying a remote direct access memory transfer from the persistent memory file system of the node to a partner node, suspending a consistency point operation until completion of the remote direct access memory transfer.
 8. The method of claim 1, comprising: maintaining snapshot creation state information comprising a first state indicating at least one of the storage file system has received a snapshot request to create the snapshot or the persistent memory file system has been notified by the storage file system that the snapshot is to be created.
 9. The method of claim 8, comprising: updating the snapshot creation state information to a second state indicating at least one of the persistent memory file system has enabled the forwarding, the persistent memory file system has initiated the framing, or the persistent memory file system has notified the storage file system that the framing is complete.
 10. The method of claim 9, comprising: updating the snapshot creation state information to a third state indicating at least one of a consistency point operation has initiated the creation of the snapshot, the persistent memory file system has been notified to create the snapshot image, the persistent memory file system has disabled the forwarding, or the consistency point operation has created the snapshot.
 11. The method of claim 1, comprising: atomically implementing a pending operation to either fully execute against the snapshot or fully execute against an active file system for which the snapshot is being created, wherein the pending operation is restricted from executing across both the snapshot and the active file system.
 12. The method of claim 1, wherein the enabling forwarding comprises: in response to receiving a modify operation at the persistent memory tier, forwarding the modify operation as a forwarded operation to the storage file system; logging the forwarded operation into a log of the node; writing the data of the forwarded operation to a target object within the storage file system; and in response to the forwarded operation being logged in the log, removing a stale copy of the target object from the persistent memory file system and performing a remote direct access memory transfer to notify a partner node that the stale copy of the target object was removed from the persistent memory file system.
 13. The method of claim 1, comprising: generating, by the persistent memory file system, the snapshot image as part of the snapshot; and adding a hierarchical reference to the snapshot image.
 14. A non-transitory machine readable medium comprising instructions, which when executed by a machine, causes the machine to: store a snapshot of a frontend file system, wherein the snapshot captures a first portion of data of the frontend file system stored within a storage device by a storage file system, and wherein the snapshot includes a snapshot image that captures a second portion of the data of the frontend file system stored within persistent memory by a persistent memory file system; in response to receiving a snapshot request to delete the snapshot, delete the first portion of the data of the frontend file system from the storage device as part of deleting the snapshot; in response to the first portion of the data being deleted, remove a reference within a namespace of the persistent memory file system to the snapshot image that is part of the snapshot; and queue the snapshot image for subsequent deletion of blocks storing the second portion of the data of the frontend file system from the persistent memory file system.
 15. The non-transitory machine readable medium of claim 14, wherein the instructions cause the machine to: process client operations while the snapshot image is queued for subsequent deletion.
 16. The non-transitory machine readable medium of claim 14, wherein the instructions cause the machine to: acknowledge the snapshot request as complete while the snapshot image is queued for subsequent deletion.
 17. The non-transitory machine readable medium of claim 16, wherein the instructions cause the machine to: subsequent to acknowledging the snapshot request as complete, traverse the persistent memory file system to free pages within the persistent memory file system that comprise the blocks of the snapshot image to delete.
 18. A computing device comprising: a memory comprising machine executable code; and a processor coupled to the memory, the processor configured to execute the machine executable code to cause the computing device to: storing data, of a frontend file system exposed for client access, across a storage device used by a storage file system to store a first portion of the data and persistent memory used by a persistent memory file system to store a second portion of the data; in response to receiving a restore request to restore the persistent memory file system and the storage file system to a state of a snapshot, fence the persistent memory file system and the storage file system to block operations directed to the persistent memory file system and the storage file system; restore the storage file system to the state of the snapshot, wherein the snapshot is used to restore the first portion of the data to the storage file system; restore the persistent memory file system to a state of a snapshot image that is part of the snapshot, wherein the snapshot image is used to restore the second portion of the data to the persistent memory file system; and unfence the persistent memory file system and the storage file system.
 19. The computing device of claim 18, wherein the machine executable code causes the computing device to: increase a reference count of the snapshot image so that an active file system points to the snapshot image.
 20. The computing device of claim 18, wherein the machine executable code causes the computing device to: in response to the computing device experiencing a failure during implementation of the restore request, clear state information within the persistent memory file system.
 21. A system comprising: a processor; and a persistent memory; and a frontend file system providing a client device with access to data stored across persistent memory used by a persistent memory file system to store a first portion of the data and across a storage device used by a storage file system to store a second portion of the data; and a node hosting the persistent memory file system and the storage file system as separate file systems, wherein the node: creates, through the storage file system, a snapshot of the storage device to include the second portion of the data of the frontend file system stored through the storage file system; and creates, through the persistent memory file system, a snapshot image to include the first portion of the data of the frontend file system stored through the persistent memory file system, wherein the snapshot image is created as part of the snapshot.
 22. The system of claim 21, wherein the node hosts a persistent memory tier that enables forwarding of modify operations from the persistent memory tier to a file system tier of the node for execution through the storage file system, wherein the forwarding is enabled in response to an indication from the file system tier that a snapshot operation is to be implemented.
 23. The system of claim 21, wherein the node hosts a persistent memory tier that initiates framing to notify the storage file system of blocks within the persistent memory file system that comprise more up-to-date data than corresponding blocks within the storage file system, wherein the framing is initiated in response to an indication from a file system tier that a snapshot operation is to be implemented. 